Multiple Scattering of Fast Electrons and Alpha-Particles, and "Curvature" of Cloud Tracks Due to Scattering

Abstract

According to a number of observers the multiple scattering of fast electrons by thin foils is appreciably less than the scattering predicted by the theory of this effect given some time ago by the present author. The statistical part of the theory, which in the earlier work was developed with special regard to the scattering of cosmic-ray particles, has been reconsidered more closely for the conditions of the experiments on fast electrons. The results confirm within a few percent the scattering given by the earlier general formula. The discrepancies must accordingly be attributed to experimental error or to a failure of the basic collision theory. A new formula is given which represents the mean projected deflection within 1 percent over the whole range of experimental conditions. The distribution of the projected deflections is considered more closely than in the earlier paper, and a general expression for the most probable deflection in space is also given. The theory is extended to the multiple scattering of $\ensuremath{\alpha}$-particles, the quantum-mechanical collision theory in this case taking the form of classical mechanics. The results are in satisfactory agreement with the early experiments of Geiger and of Mayer. A discussion is given of recent papers on the subject. Reasons are given for the nonoperation of the interference effect considered by Wheeler, and which according to him appreciably reduces the scattering. The numerical results of a new treatment of multiple scattering by Goudsmit and Saunderson are shown to be the same as those required by the general formula given by the writer's theory. Other points raised by these authors are also discussed. A summary of the theoretical results is given in Section (7).